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Community and Q&A

Reroof 3×6 T&G vaulted ceiling

kdelucas | Posted in Energy Efficiency and Durability on


I have read through many of your posts on cathedral ceilings and haven’t quite found the same situation that I have on a current remodel project on Whidbey Island, just an hour north of Seattle.  We are in Marine 4.  Our existing roof structure consists of 4×10 beams 9’ o.c. with 3×6 T&G car decking above.  There is a layer of felt on top of the decking then an existing layer of 2” rigid above that, then OSB, and composition roofing.  We are planning to remove the roofing and OSB and install 2 more layers of 2” rigid, stagger and tape the seams, add a new layer of CDX ply over that, a weather resistant barrier and a new metal roof.  We also want to keep with the look of the exposed decking on the inside.  The condition and installation of the existing rigid is an unknown.  Per our structural engineer, we do not have to install a layer of plywood directly above the car decking. (there are large spikes that tie it all together)  How do I deal with air sealing in this condition?   And which type of rigid would be best.

Thank you!


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  1. GBA Editor
    Martin Holladay | | #1

    Q. "How do I deal with air sealing in this condition?"

    A. If I were you, I would install a durable European air barrier membrane (with taped seams) or a layer of Grace Ice & Water Shield above the existing layer of 2-inch rigid foam. For more information, see "How to Install Rigid Foam On Top of Roof Sheathing."

    Q. "What type of rigid foam would be good for the new layers of rigid foam?"

    A. Either polyisocyanurate or EPS would be a good choice. For more information on this issue, see "Choosing Rigid Foam."

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